Objective lenses of the general class to which the invention relates are used for example in electron beam probing and in other spheres of application of electron beam devices, such as microscopy, inspection, lithography, etc. The high-resolution objective lenses should have low aberration coefficients particularly in the low-voltage range.
Therefore combined electric-magnetic pole piece objective lenses are known in the art which have low aberration coefficients and accordingly good low-voltage properties.
An improvement to these known objective lenses is disclosed in EP-A-0 790 634, in which the magnetic lens is formed by a single-pole lens, an electrostatic retarding lens being disposed within the magnetic lens.
The object of the invention is to improve the known objective lenses in such a way that even lower aberration coefficients are achieved.